The present invention relates generally to a composition of matter and to the use of said composition in a method for decomposing hazardous halogen-containing organic compounds, such as polychlorinated biphenyls.
The potential hazard to public health and the environment posed by the indiscriminate disposal of a variety of synthetic halogen-containing organic chemicals is well known. Compounds such as polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), decachlorooctahydro-1,3,4-metheno-2H-cyclobuta-[c,d]-pentalen-2-one (Kepone.RTM.), and 2,4,5-trichlorophenoxyacetic acid, (2,4,5-T), although having demonstrated utility, have been found in recent years to be persistent environmental poisons, and, therefore, require a safe and effective means of disposal.
The difficulty encountered in attempting to dispose of halogenated organic compounds is due in large measure to the highly stable nature of the carbon-halogen bonds present therein. The bond energy of a carbon-chlorine bond, for example, is on the order of eighty-four kcal./mole. These compounds are not only resistant to biodegradation, they cannot be degraded in a practical and effective manner by any of the well-known chemical decomposition methods. Thus, although chemical decomposition of halogen-containing organic compounds, including PCBs, has been reported, the methods employed, such as chlorolysis, catalyic dehydrohalogenation, molten salt reactions, ozone reactions, and alkali metal reduction, possess one or more significant limitations. For example, these prior art methods typically require expensive reagents, inert atmospheres, extensive temperature control, complex apparatus, substantial energy consumption, and the like. The principal problem with these methods is that they achieve incomplete dehalogenation. The impracticability of the aforementioned prior art disposal methods is evidenced by the fact that none has gained widespread acceptance by government or industry.
Incineration has also been employed as a means for disposal of hazardous chemicals but it too has certain notable drawbacks. In the first place, it requires substantial energy consumption. Hence, the expense involved in this method of disposal will probably steadily increase. Secondly, incineration requires the use of complex equipment to remove corrosive and/or toxic substances from the incinerator effluent. Thus, the expense of constructing an incineration disposal facility makes it uneconomical for those having a hazardous chemical waste disposal problem who might advantageously employ a practical disposal system. Thirdly, the residual ash formed during incineration may be toxic and present a further disposal problem.
Only a few incineration facilities are currently in operation, and some of these are in remote locations, adding excessively high transportation costs to the cost of disposal in many cases.
PCBs pose a particularly serious disposal problem. Once widely used as dielectric fluid additives in electrical equipment such as transformers and capacitors because of their excellent insulating properties, the use of PCBs were banned recently by the United States Environmental Protection Agency (E.P.A.) due to their cumulative storage in human fatty tissue and reports of extremely high toxicity. In connection with the ban, the E.P.A. has promulgated a rule whereby the available means of effective decomposition of extant PCBS and PCB-contaminated substances is limited to incineration. However, incineration of PCB-contaminated materials in accordance with E.P.A.-approved procedures is decidedly wasteful since potentially recyclable materials, such as dielectric and hydraulic fluids, which may contain a relatively small amount of PCBs are destroyed in the process. To avoid such waste, it has been proposed to treat recyclable materials contaminated by PCBs with an absorbent, e.g., by passing the material through a bed of activated charcoal or a resin to selectively remove the PCBs from said material. Although PCBs are physically removed from the recyclable material in this manner, the disposal of absorbed PCBs still remains a problem.
Aside from the PCB disposal problem, there are significant quantities of other waste or excess halogen-containing organic chemicals presently being held in storage by manufacturers, processors or consumers, which chemicals must be disposed of eventually in an environmentally acceptable manner. Viewed realistically, storage of toxic chemicals can only be considered a stop-gap measure while efforts to develop a safe, practical and effective process for their disposal continue. Storage capacity is finite, whereas the amount of hazardous chemical substances generated by industry is estimated to increase by about three percent annually.
It is apparent that a need exists for an effective and efficient process for the decomposition of halogenated organic compounds, and preferably one that is capable of (1) scavenging the hazardous substances from materials contaminated therewith, thus permitting reuse of said materials, and (2) converting the hazardous substances to useful products.